In the prior art, U.S. Pat. No. 5,079,496 in the name of the Applicant discloses a voltage regulator serving firstly to regulate the means output voltage from the alternator and secondly enabling regulation to be performed on the upper peaks of the alternator ripple included in the same signal.
The means value regulation is normally used to charge the battery at a voltage that is as uniform as possible and is close to 14.5 volts, for example.
When the voltage peaks from the alternator exceed a predetermined threshold voltage, e.g. about 19 volts, then the regulator acting on the peak values takes over from the regulator acting on the mean value to reduce the excitation current, thereby lowering the amplitude of the ripple component in the voltage. This avoids the risk of destroying the peak-clipping diodes conventionally provided in the rectifier stage at the output from the alternator. Reference may be made to the above-cited patent specification for further details on these phenomena.
Conventionally, such a regulator device is itself powered directly from the rectified output voltage from the alternator via an appropriate stabilizer stage. The power supply voltage is conventionally stabilized at about 5 volts to about 6 volts.
A drawback of this prior circuit lies in that when the rectified alternator voltage takes excessively low negative peak values, and in particular values that are lower than the above-mentioned feed voltage, then the feed voltage fails and the general operation of the regulator is severely disturbed.
The present invention seeks to mitigate this drawback and to propose a circuit of the type mentioned in the introduction which is also capable of avoiding this type of failure.
A more particular object of the invention is to achieve this result in a manner which is extremely simple and cheap.